Operators of installations for manufacturing thermoplastic containers, in particular by blow-moulding or stretch blow-moulding of heated preforms require for ever-increasing production rates. Manufacturing rates in the order of 40,000 containers per hour are currently standard today and, in view of requirements from the operators, research is now geared towards higher rates, in the order of 60,000 to 80,000 containers per hour.
As regards the supply of preforms to this type of installation, the conventional arrangements with vertical conveyor, raised hopper and chute for supplying preforms by gravity to the inlet of the installations are naturally able to satisfy the aforementioned rates currently practiced, but are no longer able to sustain the considerably higher production rates provided for the future.
Moreover, the current supply devices are of significant height which not only require very high, and thus costly factories, but also require significant additional equipment (ladders for accessing upper levels, gantries, railings, etc.) capable of ensuring the security of the personnel having to work in the upper sections.
Current research is, therefore, geared towards supply devices at ground level, preferably at waist height, so as to facilitate maintenance and supervision during operation.
It is in this context that centrifugal supply devices of the type mentioned in the preamble have been developed, also known as rotating bowl devices due to their general shape, which have a reduced height and which make it possible to supply, in particular substantially horizontal conveyors with parallel wires or belts, with preforms.
A significant problem which the devices for supplying preforms have to resolve lies in the need to remove undesirable preforms, i.e. in particular out of standard preforms not belonging to the type being treated and having in particular a diameter and/or a length which are different from those of the treated preforms, nested preforms (which may be assimilated into a preform of excessive length), etc. The removal of these undesirable preforms is extremely important as, if they are introduced into the installation for manufacturing containers, they may cause considerable damage to the installation, and even the partial destruction thereof, with the stoppage time and financial losses which are inherent with the repair and/or reconstruction of the damaged parts.
Various arrangements are known for removing undesirable preforms which are adapted to the supply devices currently in standard use, but these arrangements are not adaptable, at least in a simple manner, to the context of centrifugal supply devices.